Molecule Dynamics in Plasmonic Cavities

In metal nanostructures, coupled excitations of optical radiation and charge carriers at a metal-dielectric interface, known as plasmons, are used to confine optical radiation to regions of space orders of magnitude smaller than is possible using a dielectric cavity. This greatly enhances interactions between the light and matter, including the inelastic surface-enhanced Raman scattering (SERS) of light from molecular vibrations. In this project, the nanostructure of interest is a gold nanoparticle separated from a gold substrate by a nanoscale gap. Under laser irradiation individual gold atoms can transiently protrude into the nanocavity and further confine the optical field down to a 1nm3 volume. This can be observed through changes to the SERS spectra. In this project, work is carried out to better understand the formation of these events, the movement of metal atoms across the structure surfaces, and the direct chemical interactions with molecules within the gap. Using DNA origami, nanostructures can be assembled with complete control of the number and position of molecules within the gap. This allows the vibrational dynamics of single molecules and single molecular bonds to be observed, and provides an insight into the optomechanical properties of the system. Varying numbers of dye molecules can also be placed within the gap, allowing investigation into the resulting effect on their collective electronic and vibration coupling to light as well as their coupling to each other.